EMD SD28

The EMD SD28 was a six-axle diesel-electric road switcher produced by General Motors' Electro-Motive Division during a brief production window in the summer of 1965, with construction taking place between July and September of that year. Only six examples of the model were built for domestic American railroad service, making it one of the rarest locomotive types to emerge from EMD's La Grange, Illinois facility during the 1960s. The extremely limited production run reflected the niche position the SD28 occupied in EMD's catalog, as it was designed to offer a moderate power output in a six-axle configuration at a time when many railroads were increasingly favoring higher-horsepower turbocharged units. A closely related passenger variant, designated the SDP28, was produced for export to the Korea Railroad Corporation in May 1966, with six units delivered to that operator. The SDP28 represented an adaptation of the basic SD28 platform to meet the requirements of Korean passenger service, extending the model's reach beyond the domestic American market despite the modest overall production totals for the family as a whole. The SD28 occupies a minor but noteworthy place in the broader history of EMD's six-axle product line from the mid-1960s. Its production coincided with a period during which EMD was actively developing and marketing the turbocharged SD35, and the SD28 essentially served as a lower-powered alternative for operators who did not require the higher output that turbocharging provided. The small number of units built means the SD28 has remained a relatively obscure model in the history of American diesel motive power.

The SD28 was powered by an EMD 567D series sixteen-cylinder prime mover producing 1,800 horsepower, transmitted to the rails through DC traction motors on a C-C, or Co'Co', wheel arrangement featuring six powered axles on two three-axle trucks. The locomotive can be understood conceptually as a naturally aspirated counterpart to the SD35, sharing the same general six-axle platform but relying on a non-turbocharged version of the 567 engine family rather than the turbocharged powerplant fitted to the SD35. This distinction in the engine configuration accounted for the difference in rated output between the two models and positioned the SD28 as a more conservative choice in terms of both power and mechanical complexity. The use of the 567D engine placed the SD28 within a well-established lineage of EMD prime movers that had proven reliable in heavy railroad service since the late 1940s. The DC electrical transmission system was standard practice for EMD at the time, and the six-axle configuration provided good tractive effort characteristics suitable for road and general freight service. The SDP28 variant built for Korea incorporated a steam generator or equivalent passenger service equipment to accommodate the requirements of hauling passenger cars, representing an otherwise modest adaptation of the basic mechanical design.

—